From the past, eyeglasses and contact lenses have been prescribed for refractive errors of the eyes. These eyeglasses and contact lenses provide good vision with correction of the optical characteristics of the eyes by prescribing according to the optical characteristics of the wearer's eyes. Particularly with contact lenses, various types of research are progressing to realize better vision, and for example, many structures have been proposed from the past with goals, for example, such as improving positional stability in the circumferential direction when correcting astigmatism or presbyopia, realizing bifocal optical characteristics when correcting presbyopia, improving comfort when wearing and the like. One of the inventors of this invention also disclosed in Japanese Patent No. 3870219 (Patent Document 1), a series of combined contact lenses equipped with a novel structure in common for which there was no significant loss of vision quality even when the position on the cornea was displaced.
As can be understood from the fact that their optical characteristics are specified by the spherical lens power, the cylindrical lens power, and cylindrical lens axial direction, eye glasses and contact lenses of the conventional structure exhibit an effective corrective effect on myopia, hyperopia, presbyopia, and astigmatism. On the other hand, with this kind of eye glasses and contact lenses, even when the spherical lens power, the cylindrical lens power, and the cylindrical lens axial direction are sufficiently matched to the eyes, there may still be complaints of, “It's hard to see,” “I can't see objects well,” and the like. This kind of vision problem, which could not be put into numerical value form in the past and was due to irregular astigmatism of the eyes, was called residual irregular astigmatism.
Contact lenses having a corrective effect on this kind of residual irregular astigmatism have been researched, but it is still not possible to achieve a satisfactory effect that can be provided at the practical level. For example, residual irregular astigmatism is often due to an abnormality in the corneal surface shape, such as a conical cornea or the like, so the mainstream approach is to substantially correct the corneal shape by wearing a hard contact lens that covers the abnormal part of the corneal surface shape and pressing to correct the corneal surface shape, or forming a lacrimal lens between it and the cornea, but there are problems such as the abnormal part of the corneal surface shape being strongly pressed by the inner surface side of the hard contact lens, having wearing irritation due to the hard contact lenses, requiring expertise for the prescription, having residual irregular astigmatism newly appear deriving from the shape of the posterior surface of the cornea due to overcorrection of the irregular astigmatism due to the corneal surface shape by the hard contact lens, and the like, so a satisfactory point has not yet been reached. In light of this, in recent years, methods have been tried for reducing pressure, wearing irritation, and prescription problems by wearing wide diameter hard contact lenses which cover to the sclerocornea, but resolution of the root problem has still not been achieved. Also, there have been studies on doing shape processing of the lens surface using LASIK technology or the like, and making custom order contact lenses for handling the non-uniform corneal surface shape of each patient, but it is difficult to realize this technically without using high cost laser technology, a special precision machining lathe or the like, so practical use has not been achieved due to problems of machining technology and problems in terms of manufacturing costs.
Meanwhile, along with dramatic advances in optical and electronic analytic technology in recent years, it has become possible to do quantitative measurement using a wave-front sensor even for residual irregular astigmatism which could not be put in numerical value form in the past. By using this wave-front sensor in the optical system, for aberrations expressed by Zernike polynomials, it is possible to measure and put into numerical value form not only low order aberrations which could be corrected with conventional structure eye glasses and contact lenses, such as myopia, astigmatism and the like, but also high order aberrations that were regarded as residual irregular astigmatism in the past.
However, even if it is possible to put the residual irregular astigmatism into numerical value form with the optical system of the eye using a wave-front sensor, for example, the mode of the residual irregular astigmatism differs for each individual, so it is necessary to produce individual contact lenses having the optical characteristics for correcting that. Also, even if optical characteristics that correct irregular astigmatism at a high level of precision for each individual can be given together with a positioning mechanism for specifying the circumferential rest position in the worn state, the vision quality is unstable because it is not possible to completely control displacement of the contact lens on the cornea. Because of that, ultimately, the same as in the past, not only is it not possible to avoid problems with machining technology and problems in terms of manufacturing costs, but it is also hard to say that satisfactory vision quality is realized, and there was the problem that it is still not possible to realize a contact lens that exhibits an effective corrective effect for residual irregular astigmatism.